Neural mechanisms involved in the delay of gastric emptying of liquid elicited by acute blood volume expansion in awake rats.

We have previously reported that acute blood volume expansion in awake rats delays the gastric emptying of a liquid meal, using the phenol red method. In this study we attempted to investigate the neural mechanisms involved in this phenomenon. Blood volume expansion, due to Ringer-bicarbonate infusion up to a volume equivalent to 5% of body weight, decreased the gastric emptying of a liquid meal by half (38.2 +/- 1.8 vs 18.7 +/- 3.2%, P < 0.05). The blood volume expansion effect on gastric emptying of liquid was prevented by separate pretreatments, consisting of subdiaphragmatic vagotomy or i.v. injection of hexamethonium (20 mg kg-1) or yohimbine (3 mg kg-1). Intravenous injection of atropine (0.5 mg kg-1), guanethidine (10 mg kg-1), L-NAME (3 mg kg-1), prazosin (1 mg kg-1) or propranolol (2 mg kg-1) did not prevent the blood volume expansion effect on gastric emptying. Bilateral adrenalectomy or coeliac ganglionectomy were also ineffective. The results indicate that blood volume expansion decreases gastric emptying of liquid through vagal-dependent pathways, sensitive to hexamethonium and yohimbine. Evidence for the participation of the peripheral sympathetic nervous system was not found.